During the process of drilling and completing a well it is often desirable to remove all solid materials from the mud system in the well bore as well as removal of cement, metal and other materials which may cling to the wall of the tubular or in the case of a deviated well be laying on the side or bottom of the partially horizontal tubular. In many cases it is also desirable to change out the mud system in the well bore to a completion fluid, which is free of solids.
Currently this process is accomplished by running a tubular (commonly called a “work string”) to or near the bottom of the well. Then circulating fluid through or down this work string and into the annulus between the tubular and well bore. Circulation is accomplished by pumping fluid down the work string and back to the surface through the annulus between the work string and casing.
To assist in these process mechanical devices such as casing scrapers and brushes are attached near the bottom of the work string to remove the solids that may cling to the casing such as cement, formation debris or metal particles.
Circulation to remove the solids requires turbulent flow. In most if not all cases sufficient pump capacity is not available to accomplish the required flow rates. The flow area of the annulus is no less than 3 times and more often 5 to 10 times that of the work string. Therefore the flow rate required to maintain turbulent flow in the annulus is at least 3 times that required in the work string. By causing the solid laden fluid to flow to the surface through the work string the solids are more likely to be removed from the well due to the higher velocity fluid stream in the work string. This is particularly true in deviated wells where it is known that the mud system will “channel” and not cover the entire annular area. In these cases the solids remain in the well bore and can cause failure of packers, valves, etc. that are run in the well as a part of the completion process. These solids can also cause formation damage that prevents the well from producing at its maximum or prevents injection into the formation.
It is therefore evident to those familiar with these processes that it is desirable to move the solids to the surface by forcing them into the highest velocity flow available this being the work string.
The newest known device that represent this type of well bore clean out method is from Baker Oil Tools titled “The Well Bore Custodian” These devices are run and pulled from the well bore to remove the solids from the casing wall and place them in the mud system. Most devices require circulation to remove the solids; recognizing that circulation alone can not remove the solids, Bakers' device attempts to remove the solids by filtering them from the mud system. This device relies on the filtering system to retain the solids until the device is removed from the well. As seen in the prior art, filtering devices have been tried in the past and found not to remove all of the solids.
In the past, as illustrated in several patents, there have been a variety of tools and techniques used to remove debris. U.S. Pat. No. 2,782,860 shows the use of reverse circulation into a pickup tube held by a packer inside a tubular. Several devices involve pulling vacuum on the tubular to suck fluid and debris into it. Some examples are U.S. Pat. Nos. 3,775,805; 4,630,691; 5,269,384; 5,318,128; 3,958,651 and 5,033,545 (fluid jet creates a vacuum). U.S. Pat. No. 5,402,850 uses a seal and crossover to force fluid with debris into the annulus around the tubular string for the trip to the surface. Other techniques involve reverse flow into the tubing string, such as: U.S. Pat. Nos. 4,944,348 and 5,069,286. Also of interest are U.S. Pat. Nos. 5,562,159 and 5,718,289.